You are not stupid, at all! But it is a lot to type to explain things well. Much of this is covered on my website.
<<<<<Let's say I go to the butcher and let him cut up, grind a whole rabbit for me. That must be okay, mustn't it?>>>>
Maybe...maybe not....
Many cats in the wild do not consume an entire rabbit - ie - they do not consume all of the bones of their prey. Therefore, I question whether some of the contipation problems that we see in our whole-carcass-ground rabbit is due to there being too much bone in the diet. That is why I dilute out the whole-carcass-ground rabbit with chicken meat (no bones) and skin.
<<<In the wild cat's don't have all those extra supplements or can ask a rabbit whether it's ratio is okay.>>>>.
It is not just bone that we have to worry about. It is also the issue of taurine that is lost in processing. Google the WINN rabbit diet from UC Davis to see where cats died from cardiomyopathy when fed whole carcass ground rabbit. They ended up being taurine deficient.
<<<<So, you see, I'm still very much confused now.

>>>>
Nutrition is not always a straight-forward subject. This is why people have to do their homework when making their own cat food....and is why I spend a lot of time on the phone with people.
<<<I don't know how can food in the US is labeled. But here, in the Netherlands, calcium and phos (phosphorus or ??) are never mentioned on the labels of the can food.>>>
What we have in the states is the AAFCO lable that shows that a food is balanced for maintenance. This tells you that the Ca

hos is correct and balanced.
<<<I'm starting to wonder how to get things right...>>>>
I would just keep it very simple for now. Feed a commercial canned food with no more than 10-15% of the total diet as plain meat chunks for dental health.
If you want to get into making cat food, please go to the Making Cat Food page at catinfo.org